64 bits is still too much address for current RAM sizes, so most architectures will use less bits.
x86_64 uses 48 bits (256 TiB), and legacy mode's PAE already allows 52-bit addresses (4 PiB). 56-bits is a likely future candidate.
12 of those 48 bits are already reserved for the offset, which leaves 36 bits.
If a 2 level approach is taken, the best split would be two 18 bit levels.
But that would mean that the page directory would have 2^18 = 256K entries, which would take too much RAM: close to a single-level paging for 32 bit architectures!
Therefore, 64 bit architectures create even further page levels, commonly 3 or 4.
x86_64 uses 4 levels in a 9 | 9 | 9 | 9 scheme, so that the upper level only takes up only 2^9 higher level entries.
The 48 bits are split equally into two disjoint parts:
----------------- FFFFFFFF FFFFFFFF
Top half
----------------- FFFF8000 00000000


Not addressable


----------------- 00007FFF FFFFFFFF
Bottom half
----------------- 00000000 00000000
A 5-level scheme is emerging in 2016: software.intel.com/sites/default/files/managed/2b/80/5-level_paging_white_paper.pdf which allows 52-bit addresses with 4k pagetables.
The Linux kernel makes extensive usage of the paging features of x86 to allow fast process switches with small data fragmentation.
There are also however some features that the Linux kernel might not use, either because they are only for backwards compatibility, or because the Linux devs didn't feel it was worth it yet.
Obviously with the single intention of killing a competitor.
It is impossible to make money off WhatsApp as it is because of end-to-end encryption.
Facebook just clearly bought it to prevent it from actually growing further and killing facebook.
It is mindblowing that the sale wasn't cancelled due to anti trust.
The outcome of this is that WhatApp will remain with the same feature set forever, while other competitors have been growing, notably Discord and Slack.
Video 1.
History of Oxford University by Chris Day (2018)
Source. A large part of the video talks about how the insane system of colleges of the University of Oxford came about organically.
Aegisub by Ciro Santilli 37 Updated 2025-07-16
This worked well on 3.2.2 Ubuntu 20.10. Recommended.
First import video with:
aegisub-3.2 ourbigbook-parent.mkv
They don't have an aegisub executable without the version number. Amazing.
If you already have a subtitle file that you want to edit, then just pass it on as well:
aegisub-3.2 ourbigbook-parent.mkv ourbigbook-parent.ass
Ctrl + P: play and pause video.
Ctrl + 3: set current substitle start time.
Ctrl + 4: set current substitle end time.
Enter: finish editing the current entry and start a new one.
TODO understand better, mentioned e.g. at Subtle is the Lord by Abraham Pais (1982) page 20, and is something that Einstein worked on.

There are unlisted articles, also show them or only show them.